• Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 234
  • Last Modified:

Add IP address scope to existing scope

I have one subnet for our growing company ( that has been exhausted. I'm now getting IP address conflicts throughout the network. I would like to keep this subnet intact but expand it to: -

How easy is this done. Can I simply right-click the existing scope and change it or is there more to it?

DHCP Scope
1 Solution
Fred MarshallPrincipalCommented:
You're asking about DHCP.  And, this is a fine place to start.
First, you might ask if there are static IP addresses (like your internet gateway, servers, printers, etc.) that are currently in use.  If so, you don't want your DHCP scope to overlap.

Starting with a subnet of or /24, it seems a bit extreme to go from that (with 254 usable addresses) to one with 65532 usable addresses.  That's what you'd be getting with xxx.xxx.0.0 to xxx.xxx.255.xxx.

Now, that's all fine if all we're talking about is the subnet range.  But the question is focused on DHCP settings.
You should not be getting IP address conflicts if using DHCP in the first place.  So there must be static addresses that overlap with the DHCP address range.  That's not good or recommended practice.

Pick the size of the range that you want.  In your case, with addresses in I'd guess you have static addresses in there somewhere - above .249 perhaps like .250-.254??  And 254 usable addresses is too small it appears so what's wrong with 510 or 1022 addresses?    In some sense it doesn't matter but in terms of how you manage it and plan for further expansion, it does.  I would add more than enough and stop there.  Thus 510 or 1022 total.

If you change to or then you could set up DHCP from: (leaving 4 spares at the bottom of the range) to or or ..... leaving the current addresses in and beyond - which would preserve the static addresses (almost - see below).

Here is what I generally recommend:

1) Change the subnet of the internet gateway (and other critical routers) to match the new subnet.  
With reasonable luck, things will continue to work as long as the ranges overlap from "old" to "new" because the old IP addresses will still be on the new subnet.

2) Change the DHCP scope.

3) Cancel all the DHCP leases, forcing them to be redone.

4) Change the settings in all the statically-addressed devices to have the new subnet mask.  If the plan is done reasonably there would be no reason to change their IP addresses, just the mask.

Many things won't be affected by a mask mismatch of overlapping subnets so this might not be noticed at all in the transition.  I would still get it all done in the shortest time possible and get it done completely leaving no "old" subnet masks.
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

Featured Post

Improve Your Query Performance Tuning

In this FREE six-day email course, you'll learn from Janis Griffin, Database Performance Evangelist. She'll teach 12 steps that you can use to optimize your queries as much as possible and see measurable results in your work. Get started today!

Tackle projects and never again get stuck behind a technical roadblock.
Join Now